Without limiting the scope of the invention, the background will describe tiltrotor aircraft, as an example.
In aircraft design, many actuators are required to move certain movable elements of the craft relative to other reaction elements. One example of such a use is in the actuation of flaps on a conventional fixed wing aircraft. As in any aircraft environment, the actuator would ideally be extremely reliable, lightweight, compact and require a minimum energy input for actuation, among other requirements.
One commonly used actuator is the ball screw actuator. Generally, a ball screw actuator includes a nut with internal threads and a screw with external threads. A plurality of spherical balls are captured within the threads of the nut and engage the threads on the screw. Rotation of the nut about its center axis while resisting similar rotation of the screw will cause the screw to move axially through the nut. When the nut is mounted on a reaction element and the screw on a moving element in an aircraft, the ball screw operates as an actuator.
One type of aircraft that utilizes a ball screw actuator is the tiltrotor aircraft. Such aircraft include one or more engines that may be operated in a position that is normal for propeller driven aircraft and in a position that is normal for the rotor of a helicopter. As such, the tiltrotor aircraft can take off and land vertically, hover when desired, fly more like an airplane in level flight, and obtain speeds greater than normally possible with helicopters. The term "proprotor" is utilized herein to describe the tiltrotor airscrew since the airscrew provides the attributes of a propeller when in the level flight position and the attributes of a helicopter rotor when in the vertical position.
To achieve dual functionality, the proprotor and its associated power plant, is mounted on a pylon which can pivot on the aircraft between a conventional flight mode and a helicopter mode. In the conventional flight mode, the proprotor rotates in a vertical plane to drive the aircraft forward as in a conventional prop driven aircraft. The pylon and proprotor can then be converted or pivoted to position the proprotor in essentially a horizontal plane, where it can act as a helicopter rotor and the aircraft operated as a helicopter for vertical takeoff and landing. In such an environment, a highly reliable and efficient actuator is necessary for the proper operation of the pylon in converting between the aircraft mode and the helicopter mode.
Therefore, a need has arisen for a highly reliable system for operating the pylon between helicopter mode for take off to aircraft mode for conventional flight and back to helicopter mode for landing. A need has also arisen for such a system that includes redundant mechanical and hydraulic systems that operate in the event of partial system failures.